New Earth-sized Exoplanet is in Star’s Habitable Zone

[/caption]

An enticing new extrasolar planet found using the Keck Observatory in Hawaii is just three times the mass of Earth and it orbits the parent star squarely in the middle of the star’s “Goldilocks zone,” a potential habitable region where liquid water could exist on the planet’s surface. If confirmed, this would be the most Earth-like exoplanet yet discovered and the first strong case for a potentially habitable one. The discoverers also say this finding could mean our galaxy may be teeming with prospective habitable planets.
“Our findings offer a very compelling case for a potentially habitable planet,” said Steven Vogt from UC Santa Cruz. “The fact that we were able to detect this planet so quickly and so nearby tells us that planets like this must be really common.”

Vogt and his team from the Lick-Carnegie Exoplanet Survey actually found two new planets around the heavily studied red dwarf star Gliese 581, where planets have been found previously. Now with six known planets, Gliese 581 hosts a planetary system most similar to our own. It is located 20 light years away from Earth in the constellation Libra.

The most interesting of the two new planets is Gliese 581g, with a mass three to four times that of the Earth and an orbital period of just under 37 days. Its mass indicates that it is probably a rocky planet with likely enough gravity to hold on to an atmosphere.

The planet is also tidally locked to the star, meaning that one side is always facing the star in sunlight, while the side facing away from the star is in perpetual darkness. One effect of this is to stabilize the planet’s surface climates, according to Vogt. The most habitable zone on the planet’s surface would be on the terminator, the line between shadow and light, with surface temperatures decreasing toward the dark side and increasing toward the light side.

“Any emerging life forms would have a wide range of stable climates to choose from and to evolve around, depending on their longitude,” Vogt said.

There has been debate about the other planets found previously around Gliese 581, whether they could be habitable or not. Two of them lie at the edges of the habitable zone, one on the hot side (planet c) and one on the cold side (planet d). While some astronomers still think planet d may be habitable if it has a thick atmosphere with a strong greenhouse effect to warm it up, others are skeptical. The newly discovered planet g, however, lies right in the middle of the habitable zone.

“We had planets on both sides of the habitable zone–one too hot and one too cold–and now we have one in the middle that’s just right,” Vogt said.

The researchers estimate that the average surface temperature of the planet is between -24 and 10 degrees Fahrenheit (-31 to -12 degrees Celsius). Actual temperatures would range from blazing hot on the side facing the star to freezing cold on the dark side.

If Gliese 581g has a rocky composition similar to the Earth’s, its diameter would be about 1.2 to 1.4 times that of the Earth. The surface gravity would be about the same or slightly higher than Earth’s, so that a person could easily walk upright on the planet, Vogt said.

The planet was found using the HIRES spectrometer (designed by Vogt) on the Keck I Telescope, measuring the star’s radial velocity. The gravitational tug of an orbiting planet causes periodic changes in the radial velocity of the host star. Multiple planets induce complex wobbles in the star’s motion, and astronomers use sophisticated analyses to detect planets and determine their orbits and masses.

“It’s really hard to detect a planet like this,” Vogt said. “Every time we measure the radial velocity, that’s an evening on the telescope, and it took more than 200 observations with a precision of about 1.6 meters per second to detect this planet.”

In addition to the radial velocity observations, coauthors Henry and Williamson made precise night-to-night brightness measurements of the star with one of Tennessee State University’s robotic telescopes. “Our brightness measurements verify that the radial velocity variations are caused by the new orbiting planet and not by any process within the star itself,” Henry said.

The researchers also explored the implications of this discovery with respect to the number of stars that are likely to have at least one potentially habitable planet. Given the relatively small number of stars that have been carefully monitored by planet hunters, this discovery has come surprisingly soon.

“If these are rare, we shouldn’t have found one so quickly and so nearby,” Vogt said. “The number of systems with potentially habitable planets is probably on the order of 10 or 20 percent, and when you multiply that by the hundreds of billions of stars in the Milky Way, that’s a large number. There could be tens of billions of these systems in our galaxy.”

48 Replies to “New Earth-sized Exoplanet is in Star’s Habitable Zone”

I understand what Lawrence B. Crowell is trying to say- we don’t know hardly anything yet, there are many ways in which this planet could be a hunk of rock- but I am nevertheless very excited. I think you would have to be very jaded for this not to ignite at least some excitement or awe. There is a distinct possibility- however slight- that we, human beings, could head on over and simply stroll around on this planet! (Maybe with an oxygen breather?)

The tidal locking of this planet reduces the prospect for life. There might at best be an annular region where the star’s radiation is approximately tanget to the planet where life might exist. However, there are extreme differences of hot and cold. The atmosphere might also be in fact absent. The hot side might have the atmosphere blown away and the cold side the atmosphere might be frozen out, Over time this might leave litte atmosphere for the annular region where conditions are presumed to be right.

How does we know it it tidally locked. Well Gliese 581 has other planets like this which have been in this news. The physics can be calculated. In my book “Can Star Systems be Explored? — The physics of starprobes” I run through these caluclations with respect to previous planets found around Gliese 581.

For life to exist on this planet there has to be mechanisms that distribute the heat around the planet. This could mean horrendous storms. Otherwise I fear this planet is dead as a doornail.

I can see how the inhabitants of a tidally-locked planet would publish a book in which it categorically states that obviously you cannot have life on a rotating planets, since it it doesn’t have a stable annular ring (which is naturally the only way to support life).

Such planets will be subject to temperature changes on the order of even 40 degrees C between “Night” and “Day” (two words that scientists use to describe the periods of time of direct solar illumination and total darkness.

Seriously – given all we see on Earth regarding bio-diversity and extremophiles, I find it amazing that people still think something like a tidally locked planet is a serious barrier to life.

Wow, really exciting! I also have to agree that I don’t think it being tidally locked necessarily eliminates life. I read on New Scientist that the day side is something like 71C and the night side -40C. Couldn’t like evolve in the comfortable annular ring and then migrate outwards to the night and day regions. We certainly see extremophiles in harsher temperatures that here on Earth. However, the atmosphere being blown away/frozen out does seem concerning. But could it be regenerated? Doesn’t something like that happen on Titan? I don’t know…it’s not an area I have a lot of knowledge in. Nonetheless, very exciting. I bet the Kepler Scientists are kicking themselves that they couldn’t publish their findings sooner.

Very interesting news! It was on October 6, 1995 that the very first exoplanet was ID’d. Only 15 years later and we’ve got proof of a possible ‘Earthlike’ planet! Cool beans at a Bar-B-Que! Now, with data pouring in from the Keppler mission, we’ll no doubt have a BUNCH more candidates and proof that solar systems like ours are fairly common? ‘Drakes Equation’ may have to be revisited?

There is a bit of a critical issue here. I don’t know how atmospheres form on planets particularly, but let me conjecture two extreme cases. The first case is this planet started with a rather modest or tenuous atmosphere. If that happens there is not much heat capacity to distribute heat. So the atmosphere on the dark side freezes out and the atmosphere on the hot side evaporates off. In that case you have a dead planet. The other case is this planet has a pretty dense atmosphere. When the planet formed it was likely N_2 and CO_2, so this atmosphere trapped heat as well. So if this is two thick we might not want to compare this to a supersized Earth, but a supersized Venus. Such an atmosphere would distribute heat, but being too thick would mean it becomes a hothouse planet. Even Earth will become a Veusian type planet in 1.5 billion years or so as it is as the sun warms up.

The question comes as to whether there is a little window of opportunity for the atmosphere to be appropriate so a thousand kilometer wide strip of life could exist on the light-dark boundary. This planet is close, but I think questionable. If I had to give Jimmy the Greek odds I’d say 1:100. The one thing which is worth considering is this means there should be other planets like this around G & K class stars. Red dwarfs constitute about 60% of all stars, G-class are about 3% and K-class about 20%, where maybe half are acceptable. This means given we found this around an M-class star we should find an Earth-like planet around a more luminous star.

In a tidally locked planet, you could have a fast-evaporating ocean on the hot side, and constant rain on the night side, and all the rivers flowing from cold side into the hot side. Since the temperature gradient is persistent, this would be a hugely efficient (self regulating) heat transfer mechanism, since it relies on phase-change rather than simple convection.

And of course now you have the people living in the temperate zone being a a thermodynamic heaven… An infinite heat source to the North, an infinite heat sink to the South – what else can a civilization ask for?

You can have lifeforms that travel the water from South to North, then send spores via the atmospheric flow from North to South.

It’s my understanding that atmosphere’s are very temperature sensitive. Seems like we might have a very windy/cloudy planet with a thick atmosphere, or a dead world with much of the atmosphere frozen on the dark size and vaporized away on the hot one.

Either or, it doesn’t sound very appealing. Hopefully observations can show us that alternatives to these two scenarios are possible.

That is a possible problem. Huge thermal gradients between the two sides could cause huge winds that permanently blow. So to make the temperature distribution more even you need a thicker atmosphere with a larger heat capacity. Then the detailed trick is to avoid creating a Venusian situation.

I imagine multiple large bodies of water would help equalize temperatures. Also, wouldn’t substantial bodies of water lubricate the crust and facilitate the development of plate tectonics?

A Venusian style periodical meltdown or semi-meltdown would be pretty rough on any developing life. Furthermore, I’m uncertain how being tidally locked would effect the formation or function of tectonics, if at all.

A greenhouse effect becomes “runaway” if an increase in temperature creates an increase in the amount of greenhouse gas.

Once it does, it keeps running away until it hits the next equilibrium condition.

Where the equilibrium points are is a function of many parameters, and nothing says it’s outside the habitable condition. Earth’s atmosphere has “run away” and reached where it is today. (or rather was 100 years ago, but that’s a separate story)

With a phase-change system like I described, there will be a steady state solution (globally), and the “fast winds” will be totally normal to the inhabitants. What’s a little wind? We have creatures that live in much harsher conditions than just a little wind, even in my immediate family!

I think we ought to reign in our enthusiasm a bit here I mean we haven’t actually seen the bloody thing yet have we? All of a sudden we go from a barely detectable twitch on a screen to constructing a habitat which may or may not support life. What next, a long-lost civilisation that struggled vainly against a leaking atmosphere? Pah!

Hmm…. a “period of just under 37 days” probably means not too much of a magnetic field. That would mean that the planet has problems holding on at least to the lighter elements like the hydrogen. Consequently we have a water problem. In the worst case almost all of its atmosphere might be gone like on Mars. In the bad news department, on the hot side the atmosphere might be a bit puffed up making the loss of constituent gases even more of an issue. With its size the planet likely has some form of plate tectonics going on with volcanoes spewing out stuff on regular basis so I would be guessing that there’s at least A mechanism for replenishing the atmosphere. However, unfortunately it is likely that the wrong kind of things get replenished like on Venus. Hope I’m wrong in my scenario or at least that the planet’s gravity is enough not to let go of the hydrogen.

Well even if this planet is not nice for life, it is very promising that many other stars also have planets just like this. We know now where to look for and can now create the technology to searche for more.

I agree with Olaf: this discovery appears to dramatically improve statistics for finding habitable planets and ultimately life outside our solar system. It would just seem that systems around red dwarfs are less conducive to life then “G-type main sequence” stars such as the Sun because of planets in the habitable zone around red dwarfs having higher probability of being tidally locked to their parent stars.

Hydrazine has another interesting point. Venus rotates slower than its orbital period (224 Earth days) and has a very weak magnetic field. The Gliese 581 planet has rotation period of 37 day period. The magnetic field is generated by a dynamo action that depends on differential rotations in the interior of the planet. Consequently the magnetic field may be weak. This makes it possible if this planet started out with a modest atmosphere that it has been blasted away by the star’s energy and wind. The atmosphere might then have to be thick and dense to have prevented it from being blown off. This then means the planet could be a hot house.

There is one prospect nobody has considered though. This planet might be a double planet, similar to Earth-moon or Pluto-Charon. There is a probability that Gliese 581g or another of these Gliese planets is a double planet. If the double planet is itself tidally locked and in a ~ 1-10 terrestrial day periodicity I think the prospects for life improves considerably. So if this planet with 1.4 M_earth is two planets, say M_1 = M_earth and the other .4M_earth, then the first planet might be terrestrial like and the other a bit like Mars.

@ LC
The double planet alternative is certainly intriguing and considering the vastness of the Universe it probably does occur but how common can it be? I think it is very unlikely for two such large bodies to stay separate for any extended period of time. Pluto is smaller than the Moon which itself formed during the collision of two hypothetical planets with the sizes you propose. My point is that while possible it probably does not substantially increase the probability for finding life out there.

On the other hand, the way I see it, from the experience on our planet life is so resilient that once it gets started it perseveres. So if there ever was a window of opportunity and life did come into being it might hang on even under seemingly very adverse conditions. Then again, who are we to say what harsh conditions are. Just because we like the way Earth is doesn’t mean other worldly creatures would find them pleasant.

I am just wondering, how big would the star look like seen from the planet?
It flies very close but I do not gave figures so far. The star would not be a point like so some heat could get beyond the horizon. The planet might even wobble a bit.

I am also wondering if tidal forces could create volcano’s and actually heat the dark part too.

One possible scenario could be that water gets vaporized at the sun side, drops in frozen condition at the back side so shifting the centre point of mass and rotates slightly because of this over a few centuries. (Earth centuries) Ok I am just speculating.

Maybe rings could create a shadow at the sun site making it locally cooler.

I did a quick calculations. 3 times Earth mass, assuming that it has the same density of Earth then it would have a radius of about 1.4 times of Earth. This also means gravity would be equivalent of 1.4 times Earth.

As to how big it would look, as far as I can make out from Wikipedia, it would appear around 4 times wider (c:a 2 degrees). I base this on the fact that Gliese 581g is around 0.15AU from Gliese 581 while the star’s radius is three times smaller than the Sun’s and the Sun’s angular size is some 0.5 degrees. NOTE! This is just a quick calculation so I take no repsosibility. 😉 (But I’m pretty confident anyway.)

A question for time dilation. I know what it is but I always get confused.

Assume that I launch an spacecraft at 50% of the speed of light towards Gliese 581g.

Does this mean that ,
A: I the traveller age 20 years to get there and The Earth time moves 20*1.155 times my craft? so 23 years passed on Earth ?
B: Or does this mean that on Earth 20 years passed and I the traveller aged only 17.3 years to traverse this 20 light year distance.

Just because a planet is in the goldilocks habitable zone, doesn’t mean these guys should be celebrating and patting themselves on the backs. Venus proves the goldilocks range is over-valued, having 4 billion years of surface temperatures over 700 degrees Farenheit. Venus was supposed to be a sister earth, having nearly the same mass. a runaway greenhouse effect early in formation depleted all oxygen, trapping heat and forming excessive CO2(g). This planet by the scientists was ” INFERRED” TO HAVE a TEMPerature to support liquid water, because of its DISTANCE from the RED DWARF star (not white dwarf sun). They do NOT KNOW much of anything about exo-planet atmospheres, and how they evolve, and perhaps how rare it really is, to have an oxygen rich planet different then Venus and Mars. Perhaps CO2 greenhouse atmospheres are most common, and we struck it very lucky not to be like Mars either. More massive stars die sooner and have less time for intelligent life to evolve.

This is from my book manuscript, where I compute how long it takes to get to a certain gamma at various accelerations. There are some TeX things in here with $ and & signs and ~ which mean space, but this gives the idea. The Lorentz factor gamma = 1/sqrt(1 – (v/c)^2)

There is more in my book on this. This is tough stuff! Getting a probe to another star is not easy, and fogedabout getting people there any time in the foreseeable future. Yet this little star system would be worth send a probe to based on what we now know.

That probe would probably need a human crew since it would take 20 years to send a command or get the results. And in 20 years you could traverse a solar system visit all planets. So no ground control can control the spacecraft from here. But I would volunteer myself to go there. Even though it is only a one way ticket.

Yep, that is it. These calculations were done for a photon sail. An ion propulsion system, even if powered by a nuclear reactor, will never get you to a star in any reasonable time frame. The craft is a large strutted reflecting sheet that a large Fresnel lens concentrates solar light upon. The craft is then propelled by reflecting photon momentum. The craft is composed of three main sections, in a large 10km disk. The main section is a huge annulus, which is made of reflective thin material. Once you are at a halfway point this section detaches and is accelerated onwards by the photon beam. However, those reflected photons are concentrated on the smaller disk left behind. This decelerates this part of the craft until it reaches the destination. Then once the craft reaches the intended stellar system this truncated sail is abandoned and the third portion is the spacecraft which proceeds with its exploration of the stellar system.

This table is a bit of a “lie,” though. If you think about it, a photon powered craft will reach velocities large enough so the photons pushing it are red shifted. This then reduces the acceleration of the craft. I work this out in my book as well. By the time you reach v = .5c the acceleration is about 70% of the initial acceleration, and for v = .8c the acceleration is 40% the initial. Further, during deceleration the same problem is in effect, for the photons are being reflected off that annulus which accelerates onwards. For this reason photon propelled craft can only reach a practical limit of about gamma = 1.5 or about 70-75% the speed of light. However, this does beat the socks off of even fusion powered craft which can only plod along at about 20% light speed tops.

In my book I also discuss the relativistic rocket with much larger accelerations and to reach a gamma = 2 or v = .87c the chart appear as

If you study the chart you see the clear advantages of getting accelerations this high. The last case is one gravity acceleration and a little over a year’s time on the craft you are about a light year out. However, this requires some sort of direct conversion of matter to energy system, proverbially thought of as matter-antimatter drive that send high energy photons out the back. I discuss this technology some, and the enormous difficulties with it. I think that high energy physics and quantum black holes would be required here — which I discuss in my book. However the photon sail is clearly going to implemented before this.

I also talk about nano-bots sent electromagnetically out into space at near light speed.

As for command and control, that is a problem. I mention this as well in the book, though only in passing. I wrote this really more as a way of discussing mechanics and relativity as much as to propose sending probes to stars. A robotic probe will require something like the HAL-9000 on “2001 A Space Odyssey” capable of making decisions critical to the mission. This will largely be important once the craft enters the stellar system. Before then it is not so critical, for interstellar navigation is frankly trivial. The orbital dynamics of the Messenger on route to Mercury is much more complicated. Getting to a star is about as simple as “aim and shoot.” Mid course corrections could be relayed en route, though best done before the craft gets too far out.

Sending humans to the stars is difficult and expands the size of the craft enormously. If it takes 40 years to get to Gliese 580 you need to send food, supplies, and a living compartment of some sort. The expense grows enormously. If AI manages to increase in development we might have computers capable of making mission decisions by 2050 or so. Besides, if you think about it, even if one guy volunteers for a one way mission the whole experience could easily have all the fun of solitary confinement in a super-MAX prison facility. The person might go bonkers, a bit like “The Shining” in interstellar space.

The differences to Earth mentioned are likely not so severe that life is impossible.

A convective atmosphere will naturally give a livable annulus, the circulatory systems will be much more stable than here.

As we know from Venus a (near) locked planet retain atmosphere. The remaining water content will depend on the starting water content. (In fact, an almost sure abiogenesis inhibitor will likely be a water world, with scant nutrients at livable pressures.)

The smaller habitability volume on tidal locked annulus on habitable M worlds will be compensated by the larger frequency of M stars, so that the total habitable volume and thus the largest likelihood of life will lie in them.

Olaf: the table entries read as acceleration g, proper time, coordinate or earth time and distance

1.0 & 12.54 & 16.49 & 9.525\cr

So this is a 1m/s^2 acceleration, proper time = 12.54 years, coordinate time = 16.49 years and the distance is 9.25 light years. These are the numbers involved with reaching a gamma = 2 or v = .87c. So after 16.49 years of pushing the craft at this constant acceleration your craft will reach this speed 9.52 light years out, and the clock on the craft at this distance will report 12.54 years. So there is no travaling faster than light.

This is a good table for sending a craft to Gliese 581, about 20 light years out. If your craft accelerates for 16.49 years out you are about half way there. So if it decelerates at 1m/s^2 it will reach Gliese in 31 years or so. The g = .25m/s^2 solar sail craft could reach Gliese in a 40-50 year time frame. This might sound terribly long, but remember that the Voyager crafts have been at it for over 30 years and are still logging information.

LC. I had no idea solar sails could accelerate a craft to such velocities so quickly thank you for the links to your papers.

So what’s next?

What do you guys think is the most cost effective next steps to learning more about this planet (and other Earth analogs that will surely crop up very soon)?

I’m hoping more can be discussed about:

short/midterm: Observational tools and techniques

What can we reasonably expect to learn from this and other similar worlds in the short/medium term?

Long term: Means of sending spacecrafts.

LC mentioned using Solar sails as a very viable way of getting a probe to the Glieses system. He also mentioned we need to develop sentient or semi-sentient AI. This could be needed to handle day-to-day, or emergency operations of the craft at great distances from Earth. To me, a stable Hal like system seems like a massive challenge. Still, Ray Kurzweil in his book “A singularity is near.” makes a very logical case that such a system may be realistically possible in 40 years or so. Yet such a development opens up a radical can of worms, socially and economically.

I agree that sending a manned mission is too costly. We can send less hardware and get a probe out sooner if we subtract the technologies necessary to sustain human spaceflight.

Uncle Fred, this is not exactly a solar sail. There is a Fresnel lens that concentrates a lot of solar light on the sail. The Fresnel lens is then a huge collimator of light that points on the sail craft all the way out to its destination. An overhead projectors, not as commonly used today, with a screen looking base is a Fresnel lens. The glass plate on light house beacons is a Fresnel lens. In this way the 1/r^2 drop in irradiance from the sun is not a problem. Of course there is a host of problems, such as preventing the sail from heating up too much and maintaining the Fresnel lens aim.

A star sail could be arrived at as well. This would be enormous though. A sail-disk with about the radius of the moon with one side reflecting and the other black could literally use the momentum transfer from star light in our galaxy to accelerate to a destination.

These are the distances from previous list:
{0.0000158,4.22,4.39,4.39,5.94,7.79,8.31,8.56,8.56,8.60,8.60,9.69,10.3,10.5,10.7,10.9,11.1,11.4,11.4,11.4,11.4,11.5,11.6,11.6,11.6,11.8,11.8,11.9,12.1,12.4,12.8,12.9,13.1,13.1,13.4,13.4,13.9,13.9,14.0,14.0,14.0,14.2,14.3,14.4,14.6,14.6,14.6,14.7,14.8,14.8,14.8,15.1,15.1,15.3,15.3,15.4,15.4,15.8,15.8,15.9,16.0,16.1,16.1,16.1,16.4,16.4,16.4,16.4,16.5,16.6,16.6,16.8,17.0,17.0,17.0,17.5,17.6,17.7,17.9,18.0,18.0,18.0,18.4,18.6,18.6,18.7,18.7,18.7,18.8,18.8,18.9,18.9,19.1,19.1,19.2,19.3,19.3,19.3,19.4,19.4}

Olaf, I think you blew the return key on the page 🙂 I went through the list of planetary systems, largely considering G and upper K systems. Towards the end of working the manuscript I included the Gliese 581 because of the news then of extra-solar planets similar to Earth. I did not do much with M-class stars, because frankly I thought they were “too pud,” with tidal locking, flaring up and so forth. However, type M stars are maybe now a bit of an option. I don’t include higher F class stars on up through A B and certainly not O.

As for the cost of sending a photon sail probe to another star, that is tough to estimate. I suspect nothing like this is possible for another 50 years. I think the space infrastructure has to be considerably advanced over todays. I think building these types of structures would draw upon constructing solar power satellites composed of thin film or graphene panels. The art of strutting up these large essentially two dimensional structures is likely to develop from working up solar power from space. So if that is developed the cost factor relative to current costs might drop 2 or 3 orders of magnitude. Also the craft which makes it into the stellar system, after abandoning the sail, is not small either. It would likely be the size of our larger spacecrafts, such as the Hubble space telescope or even the space shuttle. It might weigh in at 10-100 tons.

So in the mean time we might be content with working out the foundations of cosmology.

lies lies lies
there are 80 bilion of us that is non snake seed white race on 122 planets, nasa or jpl articles are a cover up for reptyians and greys who control all 7 planets Their ships are all over the planet just put on your infra red googles. From 1990 our currant controllers/enslavers – reptilians had lost jupiter and saturn to our coming andromedan army; by 2012 they most likely be here ending the 14000 years of slavery They will be sterylazing all the Earth serpent seed evil races that is chinese jews saxons koreans turks tatars and mongols who are to agresive for the earth and when they die they souls will be taken to the distant regions possibly back to the evil orion

Universe Today Podcast

Podcast Subscription Menu

Episode 660: Crew Dragon Reaches the Station. What it Took to Replace the Space Shuttle

On Sunday, May 31st, 2020, a SpaceX Crew Dragon capsule carrying astronauts Robert Behnken and Douglas Hurley docked with the International Space Station. This was a tremendous accomplishment for SpaceX and NASA, giving the United States the capability of launching its own astronauts, and no longer relying on its Russian partners.

This was the 5th time that US astronauts went into orbit on a new kind of space vehicle, following in the footsteps of Mercury, Gemini, Apollo, and the Space Shuttle.